Study of leptonic and semileptonic kaon decays at CERN

During 2003 and 2004, the NA48/2 experiment has collected at the CERN SPS the world largest amount of charged kaon decays, with the main goal to search fo r direct CP violation in the decay of K ± into three pions. From a dedicated data sample collected in 2 004, the analysis of K ± e 3 and K ± μ 3 decay data has allowed precise measurements of the form fact ors in various parametrizations. Later, in 2007-2008, using the same detector but a modified be am and trigger logic, the NA62 experiment has taken data to measure the ratio of K → e ν and K → ν leptonic decays and has obtained a sub-percent measurement of the ratio R K = Γ ( K e 2 ) / Γ ( K μ 2 ) .